The following relates to the nuclear reactor arts, nuclear power generation arts, nuclear reactor hydrodynamic design arts, and related arts.
In nuclear reactor designs of the pressurized water reactor (integral PWR) type, a radioactive nuclear reactor core is immersed in primary coolant water at or near the bottom of a pressure vessel. In a typical design, the primary coolant is maintained in a compressed or subcooled liquid phase in a cylindrical pressure vessel that is mounted generally upright (that is, with its cylinder axis oriented vertically). A hollow cylindrical central riser is disposed concentrically inside the pressure vessel. Primary coolant flows upward through the reactor core where it is heated and rises through the central riser, discharges from the top of the central riser and reverses direction to flow downward back toward the reactor core through a downcomer annulus defined between the pressure vessel and the central riser. This is a natural convection flow circuit that can, in principle, be driven by heat injection from the reactor core and cooling of the primary coolant as it flows upward and away from the reactor core. However, in some reactor designs this natural convection is augmented or supplanted with motive force provided by electromechanical reactor coolant pumps.
To extract power from the PWR the primary coolant is flowed through a steam generator. In some designs the steam generator is external to the pressure vessel and primary coolant is fed to the steam generator through large diameter piping. In so-called “integral” PWR designs the steam generator is disposed inside the pressure vessel, typically in the downcomer annulus, and secondary coolant is flowed through the steam generator. The integral PWR design has substantial safety advantages over non-integral designs insofar as the large diameter piping carrying radioactive primary coolant to the external pressure vessel is replaced by smaller diameter piping feeding non-radioactive secondary coolant (i.e., feedwater) into the internal steam generator and extracting non-radioactive steam from the steam generator.
Some integral PWR designs conforming with the above are described in Thome et al., “Integral Helical Coil Pressurized Water Nuclear Reactor”, U.S. Pub. No. 2010/0316181 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety. U.S. Pub. No. 2010/0316181 A1 describes integral steam generators employing helical steam generator tube geometry; however, other geometries such as vertical tube designs are also known. In various steam generator designs, the primary coolant may flow inside the steam generator tubes and the secondary coolant outside the steam generator tubes, or vice versa.
Operational efficiency of such PWR systems is affected in part by the efficacy with which the upward primary coolant water flow in the central riser is reversed and transferred into downward primary coolant flow through the downcomer annulus (e.g., through a steam generator disposed in the downcomer annulus for steam generation). This flow reversal can introduce substantial flow resistance into the overall primary coolant flow circuit. Moreover, even radial and circumferential distribution of the primary coolant flow into the downcomer annulus facilitates temperature uniformity in the downcomer annulus and in the annular steam generator located therein. Various approaches have been employed for providing even radial and circumferential distribution with low flow resistance. For example, illustrative central riser of the illustrative PWR of U.S. Pub. No. 2010/0316181 A1 has an upper end that includes small openings, or a screen, that facilitates diffusion and lateral flow of primary coolant water exiting the upper orifice of the central riser. Kitch et al., U.S. Pat. No. 6,813,328 discloses another approach in which an entirely internal reactor coolant pump (RCP) submerged in the primary coolant has its discharge connected directly with the inlet of a steam generator so as to drive primary coolant exiting the upper orifice of the central riser downward into the steam generator.
Disclosed herein are improvements that provide various benefits that will become apparent to the skilled artisan upon reading the following.